Sound-amplifying projector



SOUND A/IPLIFYING PROJECTOR :2 Sinaai Filed Aug. 20: 2.920

mmm/tofu @Q13 @Mmm/mg Patented Dec. 18, 1923.

' UNITI-:D STATES PATENT OFFICE.

ELWOOD GBISSINGR, 0F BUFFALO, NEW YORK, ASSIGNR T0 LUCY ASH GRISSINGER,

. OF BUFFALO, NEW YORK.

SOUND-AMPLIFYING rRoJno'roa appiication nica august 2o, 1926.- seriai 110.464,85.

To aZZ- whom it may concern:

Be it known that I, ELwoon Griiissiimnii, a citizen of the United States and resident of Buffalo, in the county of rie and State of New York, have invented certain new and useful Improvements in Sound-Amplifying Projectors, of which the following is a specification.

My invention includes certain improvements in the sonorous reflecting pro)ectors `which are particularly adapted for employment in combination with low requency'reproducers of the types disclosed in my prior patents and applications, though they ma be alsoused in connection with the or inary standard reproducers now on the market. As described in my prior applications Serial Nos. 298,846 and 305,601, the consonant reflecting plate preferabl consists of a sheet or thin plate of soun sensitive material such as the wood used for piano sounding boards, rigidly secured to a rigid frame around the entire periphery of the plate. As contrasted with this, my present invention involves clamping the plates to the side walls at two opposite edges so as to leave these edges of the plate preferably free for vibration of maximum attainable amplitude, without danger of contacting with anything. The latter construction lias very vimportant advantages. The plate can be arranged with its clamped insensitive edges joining the side walls so that only the free vibratory edges extend crosswise in the path of the waves to be reflected, thus making the active reflecting area uniformly eastie lengthwise of the projector instead of having it crossed by non-vibratory clamped zoneslvhich are unavoidable where the crosswise edges of the plates are clamped as in my prior devices of this type. In the case of plates formed with diverging sides the tendency to omniperiodic resonant reenforcement of the sound is improved because there is less 'constraint on the plate and it can vibrate more like a set of parallel strings.

Also, a given plate of lgiven thickness,

clamped only at two opposite edges, is much more flexible and sensitive and has a lower Anatural frequency than when clamped verse resilience.

tirely free of contact with piers,

of frequencies, Aor to get a desired ratio between the wave reflecting quality and the wave absorptive and reradiating quaity, the plate can be thicker and more substantial than would otherwise be possible.

Moreover, a plate clamped about its entire periphery tends to act somewhat like a diaphragm with reference to its overtone or segmental vibrations, that is to say, its segmental vibrations are not harmonics of its fundamental but are discordant with said fundamental and with each other. When the lates a'reclamped only at two opposite e ges, however, their segmental vibrations tend to follow more nearly the harmonic law characteristic of stretched strings, that is to say, when vibrated by a note corresponding to one of their natural frequencies either fundamental or harmonic, the other natural frequencies excited thereby are harmonious and pleasing in-` stead of discordant.

By proper coordination of the various features of my invention so as to take full advantage of my above described discoveries, sound effects are "attainable which are entirely uniqueas to the loudness, vividness and perfect quality of'the reproduced sounds.

An important feature of my invention consists instressing or stretching the plates b tension. applied at the clamped edges.

his has the effect of giving the plates the stiffness factor characteristic of stretched strings, in addition to their normal trans- There are many advantages in thus tensing the plates by stretching them from the edges," particularly if the stress be carefully ap lied so that t': f plates are not bowed or ot erwise subjected to strain in directions perpendicular to the surface thereof. The much thinner metal can be employed for a given desired stiffness of plate, and while it is possible to increase the stiffness by applying the thrust of stretched strings to the back side of the plates after the manner described in my prior applications above mentioned, my present method is superior because .itn .eaves the entire area of the late orv sheet enl osts or other thrust-applying elements which tend to, produce a complicated systemof nodes and vents in the vibratory functioningfof the plates. In the present structure'the far greater tension than can be appied to perpendicular acting members and. there is therefore almost no limit to the thinness of the plateswhich I may employ. Of coursel the lighter the plates the less the inertia, the friction and the absorption of energy, and the more nearly it becomes possible to adjust the tension for sensitiveness and resonant amplification of the sound waves.

The above and other features -of my invention may be more fully understood from the following description in connection with the accompanying drawings, in

Figure 1 is a vertical section of a phonograph cabinet of ordinary construction having my improved apparatus embodied therein;

Figure 2 is a detail plan view partly in section on the line 2-2, Figure 1; I

Figure 3 is a section on line 3-3, Figure 2; t

Figure 4 is a detail perspective of the sonorous back plate with a portion ofthe plate broken away to show the frame more clearly; and

Figure 5 is a. detail view showing a corner joint of the same.

In Figure 1 the various parts of a cabinet phonograph are conventionally indicated. The case 1 has a cover 2, enclosing a shallow cavity 3, having a-bottom 4, supporting the phonograph motor case 5,.'thc rotary support 6 for the record, the tone arm swivel 8 and tone arm 9, all ot which may be of any known or desired construction.-

Communicating with the lower end of the tone arm is the upper end 11 of the tubular conduit 12 leading to the r'eflecting projector. This conduit has the forni of a frustiim of a. pyramid curved rearwardly and diverging laterally so that at the lower end, where it joins the reflecting projector, it is only a little less than the full width of' the latter. This expansion passage is preferably of gray cast iron with its walls about 3/16 inch thick so that, :icoiistically considered, it forms a natural extension of the. sound conducting passage afforded by the tone arm 9. A

The sound waves which are propagated from the lower end of conduit 12 impinge upon the sonorous reflecting plate 13 at a high angle. As shown, this angle is 115 for most of the wave front though somewhat ures 4 and 5. The mounting comprises the very substantial rigid framei20 which ma be'of spruce 3/4 inch wide by half an inc thick, or if of metal, may be of less cross section.` The side faces at 21, 21 are preferably smoothly finished so as to lie in exactly the same plane. To these faces are secured the sensitive plate 13', by' screws 22 arranged at short intervals. these screws preferably have flat under surfaces to engage squarely with thetop surface of plate 13, so astoclamp the same as rigidly as possible. The two other members of the frame are recessed at- 23 so as to 've a clearance for the ad'acentI free edges o the vibratory plate 13. llhe recessing is preferably as shallowV as the purpose will permit, a 1/32 of an inch being usually suicient. In assembling the reflecting plates with the other members of the projector, lcare is taken to securejarigid clamping. contact The heads of.

applying pressure to the plate 13 at exactly A opposite registering pointsfon th'e upper and lowersurfacesthereof, as shown at 24, 25, Figure 5.- I fin'd that this precaution is very important as contributin to proper reaction o the plates with 'reerence'to the waves impinging thereon.

In assembling the plates in the projedor, it is important to arrange the .clamped edges of the plates at the sides of the projector and to have the free edges extending transversely. As indicated in Figure 1, theossembly is such as to leave the unclamp'ed edges of the plates free of -any possible vibratoiy-con'tact with adjaoent elements and where two plates come together asfat the lower right hand vcorner in Figure 1,'it-is desirable to have one plate as' 13 extended past thelfree edge of the adjacent ilate. The uniform spacing of plate 13 is c early indicated at 18, Figure 1.

The side walls 1G of the projector mayv be of solid spruce, 1/2 to 5/8 inches in thick? ness or they may be of metal, or if desiied, they may be of resonant plate construction similar to that above described with reference to plate 13.

All of the sensitive plates may be screwed directly to the tops and bottoms of theseside walls-and all of them tensed by thrusting apart the side walls by the means hereinafter described. For convenience in manufacture, however, I have chosen to have the back plate a separate frame member as above described, and it -will be understood that any other one or more of the plates may be similar frame members. Certain .of the plates, however, and' preferably =all three of the top and bottomplates, are secured after the manner shown in Figure 3 and tension applied by extending the sides as shownin Figure 2, the back plate bein after the tensioning has been e ected.z

Referring to Figure 3,'the plate 16 i! l'ry screwed on iis rigidly secured to the side plate 16 by the screws 31 passing through suitable clamping member 32, perforations in the plate, clamping member 33, and into the side wall 1G. The clamping members 32 and 33 may be and preferably arc of metal carefully trued and the screw holes in plate 15 are carefully 'cut so as not to distort the plate. In this way a very true bearing surface and uniform clamping is insured for the edge of the plate. 'lhe other side of plate is secured to the other sidewall 16 in the same way. The opposite edges of plates 14 and 14 are secured to the bottom 15 edges of side wall 16 in the same way.

Spaced apart along the side walls are arranged opposite upstanding ears 34, 34, 35, 35, etc. The ears on the upper side are preferably spaced apart equal distances with ref- 20 erence to the length of top plate 15, and the corresponding ears on the lower side are preferably spaced apart equally with reference to the lengths Aof the respective lower plates 14 and 14". A greater or less number of these ears may be employed and they may be variously spaced tosuit special conditions. They may be integral with the side wall 16, or, as shown in the drawings, they o may be'separate members, shown in dotted 3 tain cases such ears may be formed on the ends of a solid side bar 3S, shown in dotted lines.

Of course, the side walls may be metal and the ears cast integral therewith, if desired, or the side walls being wood or other material, the ears maybe formed on a single casting.

Between the ears are thrust rods 39 threaded atthe cndand provided with nuts v'tttlx- These nuts may be screwed apart to apply any desiredtensio'n to the plates. In the form shown in the drawing the amount of tension that'can beapplied to the several plates is more'or less independent, the tension of top plate 15 beingr entirely independent of that which may be applied to 14 and 14. 11 and la are'more nearly interdependent, but even here there is widevariation between the tension that may be applied at the rear end of 14 and at the front end of 11?.

As explained in my prior applications, the reflecting plates may be of such quality and thinness that they will cause resonant reinforcement of the sound and will vibrate responsively thereto. Any vibrations thus set up in the plates cause them to be sources of re-radiated energy propagated at right angles to the surface of the plate. Mtv such waves generated by plate 13 are moedpropagated directly out of the mouth of the projector. Similar waves re-radiated from 14 will ,mosty impinge u on retlector 15 and be reflected out of t 4e pro- Cai lines at 36, and secured by screws 37. In cerjector along lines parallel with the radiation from plate 13. i

The above described arts are organized so as to afford the gr uated expansion of the wave front and application thereof to the outside air over a large area, combined with a desired distance of travel of the waves during such expansion.

A feature of -my invention which apparently contributes to the new results attained, is the employment of rolled sheet aluminum cr sheet steel for the plates. These are preferably about Nos. 16 to 25 gauge, or say 1/16 to 1/64 inch thick. The 1/16 inch plates are relatively thick and stift', but they seem to be flexible and sensitive when clamped at the side edges only. The medium and even the very thin plates seem to be better, however, when put under suficient stretching tension to give them the desired resilience or elastic stiffness. They apparently reflect a large percentage of the energy and such part of the energy as is expended in causing sympathetic vibration of the plates is re-radiated with very small loss, due to the small mass, the dense nature of the metal and the small internal friction. They seem not to use up and dissipate energy to anything like the extent that wooden plates do, even when the latter are of most carefully selected and finished material.

I claim:

1. A sound-amplifying projector having as a wall portion thereof a sheet or plate having two opposite edges each clamped between pairs of rigid, non-vibratory clamping elements and two other opposite edges free, in combination with means maintaining said plate stretched parallel with said free edges.

Q, A sound-amplifying projector having as a wall portion thereof a sonorous sheet or thin pla-te of metal having two opposite edges each cl-amped between pairs'of rigid non-vibratory clamping elements and two other opposite edges free, in combination with means maintaining said plate stretched parallel with said free ledges.

3. A sound-amplifying projector having as a wall portion thereof a sonorous sheet or thin plate of metal secured at two opposite edges and free at two other op site edges, the secured edges beinor lengthwise of the projector and the free edges transverse thereto in combination with means for stretching said plate in a direction parallel with the free edges.

4. A sound-amplifying projector having as a wall portion thereof a sonorous sheet or thin plate of metal secured at two opposite edges and free at two other opposite edges, and means for stretching said plates transversely.

5. A sound-amplifying projector having as a wall portion thereof a. sonorous sheet secured.

or thin plat-e ofmetal secured at two oppo-' site edges and free at two other op site edges, and means holding said te tightly stretched in a direction para el with the lsurface thereof.

and means for adjusting apart the portions of the projector to which. said sheets are 7. (A sound-amplifying` projector having as a wall portion thereof alsonorous sheet or thin plate of metal secured-at two opposite edges and free attwo other opposite edges, the secured edges bei lengthwise of -the lprojector and thefree e ges transverse thereto, and means forapplying stress to tension said lplates transversely. v

8. A sound-amplifying projector having as a wallportion thereof a sonorous sheet or thin plate of metal secured at two .opposite edges and free at two lother. opposite edges,

the secured edges being lengthwise of the projector -and the free eil es transverse thereto, and means for appV yin stress to said plates in a direction paralle with the surface thereof.

9. A sound-amplifying projector having as a wall portion thereof a sonorous sheet 0rthin plate of metal. secured' at two opposite edges -and free at two other opposite edges, the secured edges being lengthwise of the projector and the free edges transverse thereto, and means .for adjusting apart the portions'of the projector to which said sheets are secured. l

10. A sound-amplifying projector comprising iopposite walls and means for adjust-ably `spacing .them apart, in combination with tthin sheets of resilient metal ar ranged with opposite edges clamped to the respectiveV sides and transversely tensed by ltact with any solid body..

thrust applied to the clamping means by the adjusting means.

11. In the combination Specifiedby claim 10, the further feature of arrangin the transverse edges of said sheets free o con- 12. In the combination specified b claim Y 10, the furtherfeature of having sai plates in high-angle, sound-reflecting relation.

13. In the combination specified by claim 12, the further feature of `having at the rear end of said projector a reflecting plate adapted toprloject sound waves' upon one of said sheets at ahigh angle.

14. In the combination specified by claim 13, the further feature of having said rear plate at a proximately right angles to said sound re ector, and in combination with means for directi the sound waves on s aid back plate at a hig angle.

15. In the' combination specified by claim 14, the further feature of having an angle of approximately forty-five degrees.

16. A sound amplifying projector of'ap proxiinately rectangular cross section having Aflat divergingwalls, and means for applying tension in the plane of i, wall and'in a direction tranbverse to the axis of the pro'ector. .ff l 1 A sound'. amplifying projector of approximately rectangular cross section having flat direrging walls, and means for applying tensions to opposite walls 'in Ithe plane of each and in a. direction transverse to the axis of the projector. 18. A tion having diverging walls and means for maintaining a tension on certain of the walls in the plane thereof-and in a. plane at right a les to the axis of the rjecton i ed at Buifaioin count of Erie. and me of New York, insistir-day of August A. D. 1920.

ELwoon Gizrssr'NeEB.

projector of rectangular cnoeaeec-A 

